1. Field of the Invention
The present invention relates to exposure apparatus, movable body drive systems, pattern formation apparatus, exposure methods, and device manufacturing methods, and more particularly to an exposure apparatus used in a lithography process when electronic devices such as a semiconductor device, a liquid crystal display device and the like are produced, a movable body drive system which can be suitably used in the exposure apparatus, and measures a position of a movable body using an encoder system, a pattern formation apparatus equipped with the movable body drive system, an exposure method used in a lithography process, and a device manufacturing method which uses the exposure apparatus or the exposure method.
2. Description of the Background Art
Conventionally, in a lithography process for manufacturing electron devices (microdevices) such as semiconductor devices (such as integrated circuits) and liquid crystal display devices, exposure apparatuses such as a projection exposure apparatus by a step-and-repeat method (a so-called stepper) and a projection exposure apparatus by a step-and-scan method (a so-called scanning stepper (which is also called a scanner) are mainly used.
When exposure of a wafer is performed with these kinds of exposure apparatus, a section (an area that cannot be used as a product (chip)) which is not exposed is produced in the periphery of the wafer. However, the existence of such a section (an area) which is not exposed becomes a problem in a chemical mechanical processing (CMP) process which is applied to planarize the surface of a wafer on which a pattern is formed. Therefore, also in the past, of shot areas (hereinafter referred to as a “periphery shot”) that do not completely fit in the effective exposure area in the periphery portion of the wafer, a periphery edge exposure in which the portion which cannot be used as a device is exposed has been performed (e.g., refer to Kokai (Japanese Patent Unexamined Application Publication) No. 2006-278820)).
However, in the case of performing the periphery edge exposure separately from the exposure of transferring and forming a reticle pattern on a wafer, throughput declines due to the time required for the periphery edge exposure.
Meanwhile, as an approach for improving the throughput, various proposals are made on a twin wafer stage type exposure apparatus which employs a method where a plurality of wafer stages holding a wafer, such as for example, two wafer stages, are arranged, and concurrent processing of different operations is performed on the two stages. Recently, a proposal has been made on a twin wafer stage type exposure apparatus which employs a liquid immersion method (for example, refer to U.S. Pat. No. 7,161,659).
However, the device rule (practical minimum line width) is becoming finer, and with this, an overlay performance with higher precision is becoming required in the exposure apparatus. Because of this, a further increase is expected in the number of sample shots in Enhanced Global Alignment (EGA), which is the mainstream in wafer alignment, which may cause a decrease in the throughput even if the exposure apparatus is the twin wafer stage type exposure apparatus.
Further, in exposure apparatus such as steppers, scanners and the like, for example, position measurement of a stage holding a wafer was generally measured using a laser interferometer. However, due to finer patterns which accompany higher integration of semiconductor devices, requirements in performance is becoming tighter, and short-term variation of measurement values which is caused by air fluctuation which occurs due to the influence of temperature fluctuation and/or temperature gradient of the atmosphere on the beam path of the laser interferometer can no longer be ignored.
Therefore, recently, an encoder with a high resolution which is impervious to air fluctuation when compared with an interferometer has begun to gather attention, and inventors have proposed an exposure apparatus which uses the encoder in position measurement of a wafer stage and the like (for example, refer to the pamphlet of International Publication 2007/097379 and the like).
However, in the case of arranging a scale (a grating) on the upper surface of the wafer stage as in the exposure apparatus according to the embodiment of the pamphlet of International Publication 2007/097379 described above, there were hardly any degrees of freedom in the placement which made it difficult to create a layout, because there were many encoder heads.